Portable liquid desiccant dehumidifier

ABSTRACT

A liquid desiccant dehumidifier includes a liquid desiccant absorber arranged to receive concentrated liquid desiccant and absorb moisture contained in ambient air passed through the absorber thereby diluting the liquid desiccant. A first heat exchanger is operative to heat dilute liquid desiccant received from the desiccant absorber prior to passage to a boiler that evaporates moisture from the diluted liquid desiccant to create steam and reconstitute the desiccant into a concentrated liquid desiccant. Dilute liquid desiccant from the first heat exchanger first passes to a condenser that receives steam from the boiler and sensibly heats the dilute liquid desiccant to a higher second temperature without direct exposure to steam or air. A second heat exchanger communicates with the condenser, the boiler and the first heat exchanger and is operative to further heat diluted liquid desiccant received from the condenser to a higher third temperature prior to entry into the boiler by recovering waste heat from the boiler. A pump draws concentrated liquid desiccant from the boiler through the heat exchangers and passes it to the absorber.

This application is a continuation-in-part application of applicationSer. No. 08/984,741, filed Dec. 4, 1997.

BACKGROUND

1. Field of the Invention

The present invention relates generally to room air dehumidification,and more particularly, to a liquid desiccant dehumidifier which isportable, energy efficient, and corrosion resistant.

2. Description of the Prior Art

It is known in the art to dehumidify ambient air using liquid desiccantsystems. These devices typically utilize hygroscopic liquids such aslithium bromide (LiBr), lithium chloride (LiCl) or calcium chloride(CaCl₂) as the desiccant solution. Desiccant units offer advantages overcommercial dehumidifiers based on vapor compression technology,specifically in terms of lower energy usage.

In a desiccant system, the desiccant solution absorbs moisture fromambient air exposed to the solution. As the desiccant solution continuesto absorb moisture, it becomes dilute and must be regenerated. In theregeneration process, the desiccant solution is heated to evaporate theexcess moisture or the desiccant solution is brought into contact with ahot gas to desorb the excess moisture. In some expedients, airregenerators are used to regenerate the desiccant. These arrangementshave relatively high operating costs as energy is required to provide asource of heat and to generate a suitable flow of air. In others,boiler-type regenerators are employed. However, boiler embodiments areexpensive, as the corrosive nature of liquid desiccant solutionsnecessitates the use of costly corrosion resistant metals.

A liquid desiccant dehumidfication system in which a liquid desiccant isregenerated with a boiler is described in U.S. Pat. No. 4,939,906 ("the'906 Patent"). The '906 Patent discloses a gas-fired desiccant boilerand a combined desiccant regenerator/interchange heat exchanger, inwhich the combined regenerator/heat exchanger utilizes steam producedfrom the boiler to provide heat for partial regeneration. The desiccantboiler has a liquid/vapor separator chamber and thermosyphonrecirculation to reduce scale and corrosion of the boiler. Specifically,the overall system is shown in FIG. 1, wherein outdoor air is drawn intothe system through an inlet duct 22, and is evaporatively cooled by awater spray 24. The cooled air is directed to a desiccant conditioner 26to which return air is also directed through a duct 30. In the desiccantconditioner 26, the return air is contacted with a liquid desiccantsolution from a sprayer 28. The desiccant liquid is disclosed as lithiumcalcium chloride.

This dehumidified air is then supplied to the space to be dehumidified,or it can be sensibly cooled through an evaporative cooler 32. Thedesiccant dehumidifies the air stream, and in the process itsmoisture-absorbing capability is reduced; this capability is regeneratedby passing a portion of the dilute desiccant from the conditioner 26 toa first interchange heat exchanger 44, wherein the temperature of thedesiccant is raised. The weakened desiccant is partially concentrated inan air-desiccant regenerator 46, in which heated air from a regenerationair heater 48 contacts the liquid desiccant. This desiccant is pumpedthrough a second interchange heat exchanger 52 and thereafter to adesiccant boiler 56, in which regeneration of the desiccant iscompleted. The water vapor generated in the desiccant boiler 56 raisesthe temperature of the air passing through the regeneration airpreheater 48. The interchange heat exchangers 44, 52 reduce thetemperature of the regenerated desiccant as it returns along the pipe 60to the conditioner 26.

The boiler 56 is depicted in FIG. 2, and operates on naturalcirculation, with the density of the fluid (part liquid, part vapor) inthe "fired" tubes 70 being less than the density of the liquid in theouter "unfired" tube 74. A porous ceramic burner 80 facilitatescombustion to provide a heat source and hot combustion gases are blownthrough a combustion chamber formed by a housing 88 enclosing the firedtubes 70, and flow across fins 90 of the fired tubes 70. Weak desiccantis pumped into the fired tubes 70 through a manifold 94 which causeswater in the desiccant to be vaporized. Accordingly, a densitydifferential is created between the fluid in the fired tubes 70 and theunfired tubes 74 connected between the manifold 94 and a liquid/vaporseparator 98 outside the combustion chamber housing 88. This densitydifferential induces a natural flow of desiccant solution up the firedtubes 70 and down the unfired tubes 72. In this manner, the naturalcirculation of desiccant keeps the inside walls of the fired tubes 70coated with desiccant to thereby reduce or prevent "hot spots" fromforming on the inside of the fired tubes 70 to reduce corrosion andscale build up in the fired tubes 70.

The liquid vapor separator 98 at the top of the boiler 56 separateswater vapor from the concentrated liquid desiccant. A portion of theconcentrated desiccant is withdrawn from the bottom of the liquid/vaporseparator 98 and is returned to the desiccant conditioner 26. Watervapor flowing out of the top of the liquid/vapor separator 98 issubsequently condensed to heat air for use in an earlier regenerationstep shown in FIGS. 3 and 4.

The combined regenerator/interchange heat exchanger, depicted in FIGS. 3and 4, comprises two (2) interchange heat exchangers 44, 52, thedesiccant regenerator 46 and the regeneration air heater 48. Thecombined desiccant regenerator/interchange heat exchanger is identifiedby the reference numeral 102, and is constructed by alternately stackingtwo (2) different corrugated plates (see FIG. 4) to define alternatingflow channels. Water vapor or steam from the desiccant boiler 56 isintroduced near the top of the regenerator/exchanger 102 in alternatechannels (plate A). This water vapor is condensed, thereby transferringheat to the air and weak desiccant entering adjacent channels near thetop of the regenerator/heat exchanger 102 (plate B). The upper portionof each plate corresponds to the desiccant regenerator 46 andregeneration air heater 48. As the water vapor condenses, the weakdesiccant and air mixture is heated and the desiccant is partiallyregenerated. Warm air and moisture are exhausted by fan 106 to theoutdoors. An entrainer 108 is provided to prevent desiccant fromescaping the combined regenerator/exchanger 102. The partiallyregenerated desiccant flows into the middle of a channel plate B, and isfurther heated by the hot concentrated desiccant removed from theliquid/vapor separator 98. Hot concentrated desiccant from the boiler 56is introduced at the middle of plate A while the partially regenerateddesiccant is removed from the middle of plate B. The partiallyregenerated desiccant is then pumped to the desiccant boiler 56. Diluteddesiccant from the regenerator/heat exchanger 102 is introduced at thebottom of the plate A and is heated by the hot desiccant from the boiler56. The heated dilute desiccant from the regenerator/heat exchanger 102is then removed from the center of plate B and pumped to the top ofplate B.

The apparatus shown and described in the '906 Patent suffers fromseveral disadvantages. The regeneration process described thereinrequires the flow of hot air through the system in order to operate.This necessitates the use of additional components such as fans, airpreheaters, and liquid/vapor separators, which adds system complexity.Furthermore, the multiple stacked plate interchange heat exchangerconfiguration is complex and takes up a relatively large amount ofspace. This arrangement is not suitable for use in a small portableunit.

SUMMARY OF THE INVENTION

In view of the disadvantages in the prior art, it is an object of thepresent invention to provide a portable liquid desiccant dehumidifierwhich efficiently regenerates the liquid desiccant using a simplearrangement having a minimum number of components.

It is another object of the present invention to provide a portableliquid desiccant dehumidifier which is energy efficient.

It is still another object of the present invention to provide aportable liquid desiccant dehumidifier which utilizes primarily plasticcomponents to prevent corrosion.

It is yet another object of the present invention to provide a portableliquid desiccant dehumidifier in which steam to desiccant heat recoverytakes place in a condenser.

It is still another object of the present invention to provide aportable liquid desiccant dehumidifier in which air vents are providedon the condenser.

It is a further object of the present invention to provide a portableliquid desiccant dehumidifier in which plastic components are used forthe interchange heat exchangers.

It is yet another object of the present invention to provide a portableliquid desiccant dehumidifier in which the waste heat radiating from theboiler is utilized in an interchange heat exchanger for desiccantregeneration.

It is another object of the present invention to provide a portableliquid desiccant dehumidifier having a boiler including inner and outervessels to preheat incoming liquid desiccant entering the outer vesselwith hot liquid desiccant from the inner vessel.

It is still another object of the present invention to provide aportable liquid desiccant dehumidifier having a boiler which isprimarily elongated in a horizontal orientation to minimize thetemperature gradient and consequent concentration differential in theliquid desiccant.

It is yet another object of the present invention to provide a portableliquid desiccant dehumidifier which is lightweight, energy efficient,and inexpensive to manufacture.

It is a further object of the present invention to provide an improvedheat exchanger employing at least one polytetrafluoroethyline tubeconcentrically disposed within a silicone rubber tube.

In accordance with the foregoing objects and additional objects thatwill become apparent hereinafter, the present invention provides aliquid desiccant dehumidifier, including a liquid desiccant absorber forabsorbing moisture contained in ambient air entering the dehumidifierand passing through the desiccant absorber, the desiccant absorberconstructed and arranged for receiving concentrated liquid desiccant anddispensing dilute liquid desiccant. A boiler is provided for boilingpartially preheated dilute liquid desiccant to evaporate moisture toreconstitute the liquid desiccant into concentrated liquid desiccant. Acondenser fluidly communicates with the boiler to receive steamgenerated by boiling liquid desiccant in the boiler, and with theabsorber to receive dilute liquid desiccant from the absorber. Thecondenser and without directly exposing the dilute liquid desiccant toair is operable to sensibly heat the dilute liquid desiccant therein byrecovering the latent heat of condensation as steam delivered from theboiler is condensed, to preheat the dilute liquid desiccant prior todelivery to the boiler to increase operating efficiency.

In a preferred embodiment, the invention provides a liquid desiccantdehumidifier including a liquid desiccant absorber for absorbingmoisture contained in ambient air entering the dehumidifier and passingthrough the desiccant absorber, the desiccant absorber constructed andarranged for receiving concentrated liquid desiccant and dispensingdilute liquid desiccant. A boiler is provided for boiling partiallypreheated dilute liquid desiccant to evaporate moisture to reconstitutethe liquid desiccant into concentrated liquid desiccant. A first heatexchanger fluidly communicates with the desiccant absorber and a secondheat exchanger. The first heat exchanger is operable to transfer heatfrom the concentrated liquid desiccant to the dilute liquid desiccantdirected to the first heat exchanger from the desiccant absorber toraise the temperature of the dilute liquid desiccant to a firsttemperature. A condenser fluidly communicates with the boiler to receivesteam generated by boiling the liquid desiccant in the boiler, and withthe first heat exchanger to receive partially heated dilute liquiddesiccant from the first heat exchanger at the first temperature. Thecondenser without directly exposing the dilute liquid desiccant to airis operable to sensibly heat the dilute liquid desiccant therein to asecond temperature by recovering the latent heat of condensation assteam delivered from the boiler is condensed. The second heat exchangerfluidly communicates with the condenser, the boiler and the first heatexchanger. The second heat exchanger is operable to transfer heat fromconcentrated liquid desiccant directed to the second heat exchanger fromthe boiler to the dilute liquid desiccant directed to the second heatexchanger from the condenser at the second temperature to raise thetemperature of the dilute liquid desiccant to a third temperature. Thedilute liquid desiccant at the third temperature is directed to theboiler and the concentrated liquid desiccant from the second heatexchanger is directed to the first heat exchanger. The second heatexchanger is disposed with respect to the boiler to recover waste heatfrom the boiler. A pump is provided for pumping concentrated liquiddesiccant into the absorber.

In a preferred embodiment, the desiccant absorber includes a top and abottom and comprises: a plurality of horizontally and verticallydisposed interconnected microglass fiber plates; a distributor disposedabove the fiber plates at the top of the desiccant absorber forintroducing the concentrated desiccant into the desiccant absorber; anda drain pan for collecting the dilute desiccant disposed at the bottomof the desiccant absorber.

In another embodiment, the desiccant absorber includes a plurality ofabsorber pads disposed side-by-side, the desiccant absorber furthercomprising a top distributor pan for distributing liquid desiccant to atop side of the pads, and a drain pan for collecting dilute liquiddesiccant from a bottom side of the pan. The pads are bonded together atthe ends inside the pans. A sealant may be used to fill any gaps betweenthe pads and the pans.

The first heat exchanger comprises at least one tube assembly includingan inner tube concentrically disposed within an outer tube to define anannulus therebetween. The dilute liquid desiccant from the desiccantabsorber is passed through the inner tube, and the concentrated liquiddesiccant is passed through the annulus, or vice-a-versa.

The second heat exchanger comprises at least one tube assembly includingan inner tube concentrically disposed within an outer tube to define anannulus therebetween. The tube assembly is coiled around the boiler torecover waste heat passing through the walls of the boiler. Theconcentrated liquid desiccant from the boiler is passed through theannulus and the partially heated dilute liquid desiccant from thecondenser is passed through the inner tube, or vice-a-versa.

In a preferred embodiment, the inner tubes of the heat exchangers arefabricated from Polytetrafluoroethyline and the outer tubes arefabricated from silicone rubber. The inner tubes may be convoluted orcorrugated to increase the available heat transfer area.

In a preferred embodiment, the condenser comprises an inner shelldisposed within an outer housing defining at least one chamber betweenthe inner shell and the housing. Steam is directed to the inner shellfrom the boiler through a steam inlet. The housing includes a solutioninlet to direct partially heated dilute liquid desiccant from the firstheat exchanger into the at least one chamber. A solution outletcommunicates with the chamber and directs partially heated dilutedesiccant at the second temperature to the second heat exchanger. Theinner shell is fabricated from materials including inconel, monel,titanium, Polytetrafluoroethyline, Polytetrafluoroethyline-coatedcopper, Polytetrafluoroethyline Teflon-coated aluminum, andPolytetrafluoroethyline Teflon-coated stainless steel; and the outershell is fabricated from materials including Polytetrafluoroethyline,polycarbonate, polyvinylidene fluoride, polypropylene, silicone rubber,polyethylene, and polystyrene.

In an alternative embodiment, the condenser comprises at least one steaminlet communicating steam from the boiler with the at least one chamberand at least one solution inlet communicating partially heated diluteliquid desiccant from the first heat exchanger with the inner shell.

The condenser may incorporate a plurality of fins associated with theinner shell and a plurality of fins associated with the housing. Theinner shell may be provided with a plurality of baffles to prevent shortcircuiting from the steam inlet to the condensate outlet.

In another embodiment, the condenser comprises a housing and a pluralityof convoluted tubes. The tubes are supported by opposing support plates,and communicate with a steam inlet to receive steam from the boiler. Thehousing includes a solution inlet to receive partially heated diluteliquid desiccant from the first heat exchanger, and a solution outletthrough which partially heated dilute liquid desiccant is delivered tothe second heat exchanger. The tubes are fabricated from Teflon, and thesupport plates include at least one silicone rubber sheet attachedthereto.

In yet another embodiment, the condenser comprises at least one tubeassembly including an inner tube defining a first flow passageway and anouter tube, the inner tube being disposed within the outer tube todefine an annular second flow passageway therebetween, wherein liquiddesiccant is communicated through a first of the flow passageways andsteam is communicated through a second of the flow passageways. In analternative embodiment, the tube assembly is coiled.

In all condenser embodiments, air vents may be provided to vent air fromthe system. In a preferred embodiment, the air vent may consist ofTeflon tape laminated between a polypropylene mesh. Alternatively,conventional float-type air vents may be used.

In a preferred embodiment, the boiler includes an inner vessel and anouter vessel, a heating element disposed in the inner vessel, and a pipecommunicating heated liquid desiccant from the inner vessel and disposedwithin the outer vessel, whereby liquid desiccant is returned to theouter vessel from the condenser and is heated in the outer vessel by hotliquid desiccant passing through the pipe prior to entering the innervessel.

In an alternative embodiment, the boiler includes an inner vessel and anouter vessel, a heating element disposed in the inner vessel, and aninterchange heat exchanger disposed in the outer vessel. The interchangeheat exchanger includes an inner tube and an outer tube defining anannulus therebetween, and an inlet disposed to admit desiccant rising tothe top of a desiccant puddle in the outer vessel to enable heattransfer with hot desiccant leaving the inner vessel. In this manner,liquid desiccant returned to the outer vessel from the condenser ispreheated in the outer vessel and the interchange heat exchanger priorto entering the inner vessel.

In a preferred embodiment, the respective components are disposed withrespect to one another to take advantage of gravity feed to communicatethe liquid desiccant from the absorber to the boiler via the first andsecond heat exchangers and the condenser, thereby eliminating the needfor multiple pumps in the system.

BRIEF DESCRIPTION OF THE DRAWINGS

In accordance with the above, the present invention will now bedescribed in detail with particular reference to the accompanyingdrawings.

FIG. 1 is an exploded isometric view of the portable liquid desiccantdehumidifier in accordance with the present invention;

FIG. 1A is a block diagram depicting the general operation of theinvention;

FIG. 2 is an exploded isometric view of a desiccant absorber assembly;

FIG. 2A is a detail view of the microglass fiber plates in the absorber;

FIG. 2B is a side elevational view of a desiccant absorber in anotherembodiment;

FIG. 2C is a detail view of the absorber pads;

FIG. 2D is an isometric view of the desiccant absorber of FIG. 2B;

FIG. 3 is an isometric view of a boiler;

FIG. 4 is a an isometric view of a coiled interchange heat exchanger andthe boiler;

FIG. 4A is an isometric view of a boiler in an alternative embodiment;

FIG. 4B is an isometric view of a boiler in another embodiment;

FIG. 5 is an isometric view of a split interchange heat exchanger;

FIG. 5A is a plan view of an inner tube for an interchange heatexchanger having a convoluted profile;

FIG. 5B is a plan view of an inner tube for an interchange heatexchanger having a corrugated profile;

FIG. 6 is an isometric cut-away view of a condenser in a firstembodiment;

FIG. 7 is an isometric cut-away view of an inner shell of the condensershown in FIG. 6;

FIG. 8 is an isometric cut-away view of a condenser in a secondembodiment;

FIG. 9 is an isometric cut-away view of a condenser in a thirdembodiment;

FIG. 9A is an isometric view of a condenser in a fourth embodiment;

FIG. 9B is an isometric view of a condenser is a fifth embodiment;

FIG. 10 is an isometric cut-away view of a frame for housing therespective components of the system; and

FIG. 11 is an isometric cut-away view depicting the frame and some ofthe components installed therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the several views of the drawings, there is shown aportable liquid desiccant dehumidifier ("PLDD"), generally characterizedby the reference numeral 10.

Referring now to FIGS. 1 and 1A, the PLDD 10 includes a liquid desiccantabsorber 12 for absorbing moisture contained in ambient air enteringdehumidifier 10 and passing through desiccant absorber 12. The desiccantabsorber 12 is constructed and arranged for receiving concentratedliquid desiccant at the top of desiccant absorber 12 and dispensingdilute liquid desiccant from the bottom of desiccant absorber 12. Thedesiccant solution may be any one of several conventional solutions,including aqueous LiBr, LiCl or CaCl₂, as described above, or anymixture of these solutions. Referring now to FIGS. 2 and 2A, desiccantabsorber 12 includes a distributor 14 disposed at the top of desiccantabsorber 12 which receives concentrated liquid desiccant and deliversthe liquid desiccant through a plurality of "spaghetti" tubes 16extending radially outward from a central hub 18. The desiccant absorber12 includes a plurality of horizontally and vertically disposedinterconnected microglass fiber plates. The vertical plates areidentified by the reference numeral 20, and are supported by horizontalinterconnecting fiber plates 22 as shown. The top plate 22 is referredto as a distribution sheet. The concentrated desiccant wicks into thedistribution sheet 22 and down the vertical plates 20. The verticalplates 20 contain beads 21 which separate and support contiguousvertical plates 20. Ambient air is drawn into the unit and forcedthrough the microglass fiber plates by a fan 23 (see FIG. 1), where themoisture in the air is removed as the air makes contact with the liquiddesiccant. As the desiccant dehumidifies the air stream, themoisture-absorbing capability of the desiccant is reduced and thedesiccant must be regenerated. This dilute desiccant is collected in adrain pan 24 disposed at the bottom of desiccant absorber 12. The drainpan 24 includes an intermediate support plate 26 defining at least onedrain hole 28 which enables the dilute desiccant to flow into a bottomchamber defined between support plate 26 and a bottom wall 30 of drainpan 24. A drain tube 32 including a one-way or check valve 33 extendsfrom the bottom chamber to direct the dilute desiccant out of absorber12. The absorber components are disposed within a frame 35 as shown inFIG. 10, which can be fabricated from materials including, but notlimited to, polypropylene, polyethylene, polytetrafluoroethyline, whichis commercially available under the tradename TEFLON, polyvinylidenefluoride, polycarbonate, PVC or polystyrene. The frame 35 includes aplurality of shelves 37a, 37b, and 37c for supporting the respectivecomponents of the unit described below.

The dilute liquid desiccant is regenerated into concentrated desiccantby boiling the liquid desiccant in a boiler 34 at a temperature in therange of from approximately 260° F. to 320° F. An improvement over priorart systems resides in the use of steam to desiccant heat recovery todirectly preheat the dilute liquid desiccant. The dilute liquiddesiccant is thus passed through a condenser and preheated using thelatent heat of condensation of the steam produced by boiling the liquiddesiccant. Preferably, a series of interchange heat exchangers areemployed to further preheat the dilute liquid desiccant entering theboiler 34 by recovering heat from the concentrated liquid desiccantdelivered to absorber 12 from boiler 34 to further increase operatingefficiency. These components are described in more detail below.

In an alternative embodiment shown in FIGS. 2B-2D, a plurality ofabsorber pads 20a are stacked side-by-side. The pads 20a are received inan aperture or slots in a top tray or distributor pan 25 and a bottomtray or drain pan 27. The pads 20a are bonded to each other at the endsthereof with an adhesive "A" (or taped) so that the gaps between thepads 20a and the supporting structure are completely sealed to force theliquid desiccant to wick through the pads 20a. Any other gaps betweenthe pads 20a and the pans 25, 27 may be filled with an RTV siliconesealant or like material. Liquid desiccant is communicated into thedistributor pan 25 through an inlet 29. This configuration prevents theliquid desiccant from just flowing over the surface of the pads, andconsequently increases absorber efficiency. The trays 25, 27 effectivelyprevent spillage of liquid desiccant from the absorber 12 in the eventof tilting. In addition, the liquid desiccant supplied to thedistributor pan 25 forms a thin film on the pan surfaces to reach everydistributor pad 20a to improve desiccant distribution.

The boiler 34 is shown in FIG. 3, and is configured in the shape of atub or vessel having an elongated horizontal dimension. The horizontalelongation provides a uniform temperature gradient, and thus a uniformconcentration level of the liquid desiccant solution, as compared to avertically elongated boiler. The boiler 34 includes side walls 36, abottom wall 38, a top wall 40, and a peripheral support flange 42 forsupporting the other dehumidifier components above the boiler. Theboiler 34 is constructed from materials including, but not limited to,polycarbonate, polyvinylidene fluoride, Teflon, fiber glass and thelike. A heating element 44 is coiled proximal to the bottom wall 40 asshown, and is connected to a pair of leads 46 in a conventional manner.A thermocouple 48 extends into boiler 34 to monitor the internaltemperature. The leads 46 and thermocouple 48 extend through top wall40. The heating element 44 and thermocouple 48 are operably associatedwith a controller (not shown) for maintaining boiler 34 at the optimumtemperature. A pair of steam outlets 50 extend through top wall 40 todeliver steam generated by boiling the liquid desiccant to a condenserdescribed in more detail below.

Referring now to FIG. 4, a drain tube 51 is coupled to one of the sidewalls 36 to enable boiler 34 to be emptied as required. A U-fitting 52is coupled to the upper region of one of the side walls 36 to receivepreheated dilute liquid desiccant from the condenser through an inletport 54, and to dispense concentrated liquid desiccant through an outletport 56. The U-fitting 52 communicates with a coiled interchange heatexchanger 58, which comprises at least one tube assembly including aninner tube 60 concentrically disposed within an outer tube 62 to definean annulus 64 therebetween. The tube assembly is coiled around boiler 34to recover the waste heat radiating through side walls 36. Thisarrangement is exemplary, as the tube assembly could be embedded withinthe side walls 36, or disposed in contact with top wall 40. Theconcentrated liquid desiccant from boiler 34 enters the annulus 64through side wall 36 and is directed to outlet port 56. The partiallyheated dilute liquid desiccant from the condenser is passed through theinner tube 60 in a direction counter to the concentrated liquiddesiccant and enters boiler 34 through side wall 36. Alternatively, theconcentrated liquid desiccant is passed through inner tube 60 and thedilute liquid desiccant is passed through annulus 64. In a preferredembodiment, inner tube 60 is fabricated from TEFLON, and outer tube 62is constructed from silicone rubber. The TEFLON inner tube 60 hasrelatively high heat conductivity, while the outer silicone rubber tube62 has a relatively low thermal conductivity, and is a good insulator.These components can withstand relatively high temperatures (˜400° F.),and are not corroded by the desiccant solution. To improve efficiency,inner tube 60 may be convoluted as shown in FIG. 5A or corrugated asshown in FIG. 5B. It is to be understood that the use of this type ofTEFLON/silicone rubber tube-in-tube heat exchanger is not limited to aliquid desiccant system. There are many applications in which thisarrangement may be employed. The particular operation of the coiledinterchange heat exchanger 58 will be described in more detail below.

Referring now to FIG. 4A, there is shown an isometric view of an boiler34a in an alternative embodiment, having a double-wall configurationincluding an inner wall 400 and an outer wall 402 which define an innervessel 404 and an outer vessel 406. A heating element 408 extends intothe inner vessel 404 and around the floor as shown. The incoming liquiddesiccant from condenser 86 enters the outer vessel 406 of the boiler atinlet 410. Hot liquid desiccant from the inner vessel 404 iscommunicated into pipe 412 which coils through the outer vessel 406 toeffect heat transfer with the incoming liquid desiccant. The desiccantpuddle contained in the outer vessel 406 is heated and the hottestportion of the liquid is forced to rise to the top of the vessel 406. Itis then fed into the inner vessel 404 via an inlet 414. A thermocouple416 is disposed in the inner vessel 404 as described above to controlthe boiler temperature. This arrangement forces any heat radiated orconducted from the inner vessel 404 to flow through the desiccant puddlein the outer vessel 406, thereby reducing thermal losses, and pressurelosses attributable to long flow paths. The heating element 408 isdisposed below the pump suction or inner vessel boiler outlet 415a sothat heating element 408 is always immersed in a pool of liquiddesiccant within the inner vessel 404. In this manner, the pump 80 stopsdrawing liquid desiccant from inner vessel 404 before it is reduced to alevel beneath the heating element 408. Hot liquid desiccant leaves theboiler through outlet 415b. This arrangement eliminates the need for alow-level control switch. High level control in the boiler is necessaryto provide consistent dehumidification and to prevent excess liquidbuildup. A high level control switch can be eliminated by sizing theinner vessel 404 with an internal volume equal to approximately twicethe volume of pooled liquid desiccant accumulation. This takes advantageof the inherent desiccant properties to make the system flexible toadapt to varying weather conditions without compromising performance.

Referring now to FIG. 4B, there is shown an isometric view of a boiler34b in an alternative embodiment, having a double-wall configurationincluding an inner wall 400b and an outer wall 402b which define aninner vessel 404b and an outer vessel 406b. A heating element 408bextends into the inner vessel 404b and around the floor as shown. Theincoming liquid desiccant from condenser 86 enters the outer vessel 406bof the boiler at inlet 410b. An interchange heat exchanger 412a isdisposed within the outer vessel 406b. The interchange heat exchangercomprises an inner tube 407a and an outer tube 407b defining an annulustherebetween. The tube arrangement may be similar to that describedabove with the inner tube being either convoluted or corrugated toimprove heat transfer characteristics. An inlet 417 permits liquiddesiccant to enter the annulus between inner tube 407a and the outertube 407b. This liquid desiccant has been preheated by heat transferbetween the inner vessel 404a and the outer vessel 406b. The hottestportion of the heated liquid desiccant in the outer vessel is forced torise to the top of the puddle, and enters the interchange heat exchanger412a through inlet 417. Hot liquid desiccant from the inner vessel 404bis communicated into the interchange heat exchanger 412a at outlet 415ato effect heat transfer with the incoming liquid desiccant. Thepreheated liquid desiccant is then fed from the interchange heatexchanger 412a into the inner vessel 404a via an inlet 414a. Athermocouple 416 is disposed in the inner vessel 404a as described aboveto control the boiler temperature.

Referring now to FIG. 5, there is depicted a split interchange heatexchanger 66, which includes a pair of tube assemblies 68. Each tubeassembly 68 comprises an inner tube 70 concentrically disposed within anouter tube 72 to define an annulus 74 therebetween. The dilute liquiddesiccant from desiccant absorber 12 is gravity fed to the interchangeheat exchanger 66, where it is directed through a manifold 76 and intothe inner tubes 70. Concentrated liquid desiccant from boiler 34 isfirst delivered through coiled interchange heat exchanger 58 andthereafter directed through a U-fitting 78 coupled to the respectiveouter tubes 72 and into the annuli 74. Alternatively, dilute liquiddesiccant is passed through annuli 74 and concentrated liquid desiccantis passed through inner tubes 70. In this manner, heat is transferredfrom the concentrated liquid desiccant to the dilute liquid desiccantwithin split interchange heat exchanger 66. The concentrated liquiddesiccant is thereafter drawn into a pump 80 (see FIGS. 1 and 1A)through a U-fitting 82 coupled to the respective outer tubes 72. Thepump 80 delivers the concentrated liquid desiccant to distributor 14 ofabsorber 12. The partially heated dilute liquid desiccant flows througha manifold 84 to the condenser. During this stage, the dilute liquiddesiccant dispensed from absorber 12 is raised to a first temperature.As discussed above with respect to coiled interchange heat exchanger 58,the inner tubes 70 may be fabricated from TEFLON and the outer tubes 72may be constructed from silicone rubber. Likewise, the inner tubes maybe provided with a convoluted or corrugated profile as shown in FIGS. 5Aand 5B, respectively.

The partially heated liquid desiccant at the first temperature isdelivered to a condenser 86 from split interchange heat exchanger 66 asshown in FIGS. 1 and 1A. Referring now to FIGS. 6 and 7, there isdepicted a first embodiment of condenser 86, which is comprised of aninner shell 88 disposed within an outer housing 90 defining at least onechamber 92 between inner shell 88 and housing 90. The housing 90includes a plurality of side walls 94, a top wall 96 and a bottom wall98. A pair of steam tubes 100 communicate with inner shell 88 throughtop wall 96 to deliver steam from boiler 34. A pair of air vents 102likewise communicate with chamber 92 through top wall 96 to evacuateexcess air therefrom. A condensate tube 104 communicates with innershell 88 through bottom wall 98 to drain condensate into a condensatepan 106 (see FIG. 1A). An inlet tube 108 communicates with chamber 92through one of the side walls 94 to deliver partially heated dilutedesiccant to condenser 86 from split interchange heat exchanger 66. Anoutlet tube 110 is similarly disposed to communicate with chamber 92 onan opposite side of condenser 86 to deliver dilute desiccant which issensibly heated to a second temperature by the latent heat ofcondensation as the steam condenses in the inner shell 88, to the coiledinterchange heat exchanger 58 via the inlet port 54 of U-fitting 52shown in FIGS. 1 and 4. A fraction of the desiccant flow leaving thecondenser may be recirculated to the desiccant absorber 12. This reducesthe flow rate to the boiler 34 to lower heat loss and increase energyefficiency. In addition, this maintains a relatively high flow throughthe absorber 12 and condenser 86 to yield a higher absorption andcondensation capacity. To facilitate heat transfer, inner shell 88 isfabricated from materials including inconel, monel, titanium, TEFLON,TEFLON-coated copper, TEFLON-coated aluminum, and TEFLON-coatedstainless steel. The housing 90 is fabricated from materials includingTEFLON, polycarbonate, polyvinylidene fluoride, polypropylene, siliconerubber, polyethylene, and polystyrene. If a plastic such as TEFLON isused for the housing 90, the wall thickness is made suitably thick toprovide the necessary insulating properties.

The condenser 86 may incorporate a plurality of fins 112 located on theexterior of inner shell 88 and a plurality of fins 114 disposed onbottom wall 98 of housing 90. The inner shell 88 may be provided with aplurality of baffles 116 to prevent short circuiting from steam inlets100 to condensate outlet 104.

Although depicted with the steam being directed into the inner shell 88and the liquid desiccant being directed into the chamber 92, theopposite arrangement may be employed with the liquid desiccant directedinto the inner shell 88 and the steam delivered to the chamber 92.Referring now to FIG. 8, there is shown an alternative embodiment of acondenser 86a, including a housing 90a and inner shell 88a, where theinner shell 88a segregates housing 90a into two compartments 92a, 92b,respectively. A steam inlet tube 100a communicates with compartment 92a,and a steam inlet tube 100b communicates with compartment 92b. Partiallyheated dilute desiccant solution is delivered to inner shell 88a throughsolution inlet 108a, and is sensibly heated by the latent heat ofcondensation as the steam condenses in the respective chambers 92a, 92b.Condensate flows out of chambers 92a, 92b, via condensate outlets 104a,104b, respectively. Partially heated dilute desiccant at the secondtemperature flows out of inner shell 88a through solution outlet 110a tocoiled interchange heat exchanger 58. Baffles 112a, 112b are provided inchambers 92a, 92b, respectively.

Referring now to FIG. 9, there is shown a third embodiment of acondenser 86b, comprising a housing 90b and a plurality of tubes 118,which may be convoluted or corrugated as described above with regard tothe interchange heat exchangers and shown in FIGS. 5A and 5B. The tubes118 are supported by opposing support plates 120 and communicate withrespective steam inlets 100c, 100d through which steam is delivered fromboiler 34. The housing 90b includes a liquid desiccant solution inlet108b to receive dilute liquid desiccant from split interchange heatexchanger 66, and an outlet 110b to deliver partially heated liquiddesiccant at the second temperature to the coiled interchange heatexchanger 58. The tubes 118 are fabricated from TEFLON, and the supportplates 120 include at least one silicone rubber sheet attached thereto.

Referring now to FIG. 9A, there is shown another embodiment of acondenser 86c, utilizing multiple double-pipe heat exchangers. Eachdouble-pipe heat exchanger comprises an outer straight tube 300 and aninner convoluted tube 302 concentrically disposed within the outer tube.A small annular gap is defined between the outer and inner tubes 300,302 which forces the fluid to follow a "screw-like" tortuous paththrough the convolutions at high velocity. This arrangement provideshigh heat transfer coefficients and condensation capacity. Thecomponents can be fabricated from plastics such as polypropylene,TEFLON, PVDF or silicone rubber. Dilute liquid desiccant from splitInterchange heat exchanger 66 is directed into a manifold 304.Similarly, steam from boiler 34 flows into a manifold 306 through inletports 308. Manifold 304 communicates with the inner convoluted tubes302. Steam flows through the annuli formed between outer tubes 308 andinner tubes 302, causing the dilute liquid desiccant entering the heatexchangers from manifold 304 to be partially heated to the secondtemperature. This heated liquid desiccant is delivered to the coiledinterchange heat exchanger 58 from exit manifold 310. Condensate iscollected in manifold 312, and is then delivered to pan 106. Air ventsare utilized to ensure reliable gravity assisted drain flow of theliquid desiccant from the absorber 12 to the boiler 34. In a preferredembodiment, small pieces of TEFLON tape having a micro-pore structurecan be used in the vent assembly. The TEFLON material is hydrophobic andhas a micro-pore structure which enables the free passage of air whilepreventing desiccant leakage. The air vent 314 comprises a tube 316extending upwardly from manifold 310. The tube 316 includes apolypropylene mesh 318 and a piece of TEFLON tape 320 in a laminatedstructure. Alternatively, conventional float-based air vents, such asair vents manufactured by Honeywell, can be utilized to vent air fromthe system.

Referring now to FIG. 9B, in another embodiment the condenser 86dcomprises multiple coiled double pipe heat exchangers. Each double pipeheat exchanger includes an outer straight tube 300a and inner convolutedtube 302a concentrically disposed within the outer tube 300a. Steam fromboiler 34 enters a manifold 306a, from where it is communicated into theannuli formed between outer tubes 300a and inner tubes 302a. Diluteliquid desiccant is delivered to manifold 304a and thence into the innertubes 302a. Partially heated liquid desiccant exits into manifold 310a,and is delivered to coiled Interchange heat exchanger 58. Condensateflows through outlets 312a to pan 106. This condenser 86d, operates onthe same principles and offers the same advantages as the double-pipecondenser 86c described above.

Referring now to FIG. 11, the respective components of the PLDD 10 areshown stacked within frame 35.

During the operating cycle, ambient air is drawn into the unit, throughabsorber 12 and exhausted to the room by fan 23. The moisture in the airis extracted as the air makes contact with the liquid desiccant wickingacross the microglass fiber wick plates 20, 22. Dilute liquid desiccantis gravity fed from drain pan 24 of absorber 12 to manifold 76 of splitinterchange heat exchanger 66, wherein it is raised to a firsttemperature through heat transfer from concentrated liquid desiccantflowing through annuli 74. The dilute liquid desiccant at the firsttemperature is then delivered to the condenser 86, in which the latentheat of condensation as the steam condenses sensibly heats the liquiddesiccant to the second temperature. The liquid desiccant at the secondtemperature is thereafter delivered to the coiled interchange heatexchanger 58 in which it is further heated to a third temperature priorto introduction into boiler 34 for regeneration. The coiled interchangeheat exchanger 58 recovers waste heat radiating from the walls 36 ofboiler 34. The concentrated liquid desiccant solution produced byboiling the liquid desiccant is drawn through the coiled interchangeheat exchanger 58 and split interchange heat exchanger 66, andthereafter delivered to distributor 14 of absorber 12 by pump 80. Thestacking of the respective components as shown in FIG. 1 provides forthe gravity feed of dilute liquid desiccant from absorber 12 to boiler34 through the first and second heat exchangers and the condenser,thereby eliminating the need for multiple pumps in the system.

The present invention has been shown and described in what areconsidered to be the most practical and preferred embodiments. It isanticipated, however, that departures can be made therefrom and thatobvious modifications will be implemented by persons skilled in the art.

What is claimed is:
 1. A liquid desiccant dehumidifier, comprising:aliquid desiccant absorber for absorbing moisture contained in ambientair entering the dehumidifier and passing through said desiccantabsorber, said desiccant absorber constructed and arranged for receivingconcentrated liquid desiccant and dispensing dilute liquid desiccant,said desiccant absorber including a plurality of absorber pads disposedin upstanding side-by-side relation, said desiccant absorber furtherincluding a distributor pan disposed above said pads for distributingliquid desiccant to said pads, said absorber pads being secured togetherat least adjacent upper ends thereof so as to substantially preventliquid desiccant from said distributor pan passing downwardly betweensaid pads and thereby cause said desiccant to wick downwardly throughsaid pads, and a drain pan disposed below said pads for collectingdilute liquid desiccant from said pads; a boiler for boiling diluteliquid desiccant to evaporate moisture to reconstitute the liquiddesiccant into concentrated liquid desiccant; and a condenser fluidlycommunicating with said boiler to receive steam generated by boilingliquid desiccant in said boiler, said condenser further fluidlycommunicating with said absorber to receive dilute liquid desiccant fromsaid absorber, said condenser being operable to sensibly heat the diluteliquid desiccant therein by recovering the latent heat of condensationas steam delivered from said boiler is condensed so as to preheat saiddilute liquid desiccant prior to delivery to said boiler.
 2. A liquiddesiccant dehumidifier as defined in claim 1 wherein said absorber padsare bonded together in spaced sealed relation at said upper ends thereofso as to prevent liquid desiccant from passing downwardly between saidpads.
 3. A liquid desiccant dehumidifier as defined in claim 1 whereinsaid upper ends of said absorber pads are received in slots formed insaid distributor pan in sealed relation with said pan so that liquiddesiccant flows only into said pads from said pan.
 4. A liquid desiccantdehumidifier, comprising:a liquid desiccant absorber for absorbingmoisture contained in ambient air entering the dehumidifier and passingthrough said desiccant absorber, said desiccant absorber constructed andarranged for receiving concentrated liquid desiccant and dispensingdilute liquid desiccant, a boiler for boiling partially preheated diluteliquid desiccant to evaporate moisture to reconstitute the liquiddesiccant into concentrated liquid desiccant, said boiler including aninner vessel and an outer vessel, a heating element disposed in saidinner vessel, and a pipe communicating heated liquid desiccant from saidinner vessel and disposed within said outer vessel, whereby liquiddesiccant is returned to said outer vessel from said condenser and isheated in said outer vessel by hot liquid desiccant passing through saidpipe prior to entering said inner vessel; and a condenser fluidlycommunicating with said boiler to receive steam generated by boilingliquid desiccant in said boiler, said condenser further fluidlycommunicating with said absorber to receive dilute liquid desiccant fromsaid absorber, said condenser being operable to sensibly heat the diluteliquid desiccant therein by recovering the latent heat of condensationas steam delivered from said boiler is condensed, to preheat said diluteliquid desiccant prior to delivery to said boiler.
 5. A liquid desiccantdehumidifier, comprising:a liquid desiccant absorber for absorbingmoisture contained in ambient air entering the dehumidifier and passingthrough said desiccant absorber, said desiccant absorber constructed andarranged for receiving concentrated liquid desiccant and dispensingdilute liquid desiccant, a boiler for boiling partially preheated diluteliquid desiccant to evaporate moisture to reconstitute the liquiddesiccant into concentrated liquid desiccant, said boiler including andinner vessel and an outer vessel, a heating element disposed in saidinner vessel, and an interchange heat exchanger disposed in said outervessel, said interchange heat exchanger including an inner tube and anouter tube defining an annulus therebetween, said interchange heatexchanger including an inlet disposed to admit desiccant rising to thetop of a desiccant puddle in said outer vessel to enable heat transferwith hot desiccant leaving said inner vessel, whereby liquid desiccantreturned to said outer vessel from said condenser is preheated in saidouter vessel and said interchange heat exchanger prior to entering saidinner vessel; and a condenser fluidly communicating with said boiler toreceive steam generated by boiling liquid desiccant in said boiler, saidcondenser further fluidly communicating with said absorber to receivedilute liquid desiccant from said absorber, said condenser beingoperable to sensibly heat the dilute liquid desiccant therein byrecovering the latent heat of condensation as steam delivered from saidboiler is condensed, to preheat said dilute liquid desiccant prior todelivery to said boiler.
 6. A liquid desiccant dehumidifier,comprising:a liquid desiccant absorber for absorbing moisture containedin ambient air entering the dehumidifier and passing through saiddesiccant absorber, said desiccant absorber constructed and arranged forreceiving concentrated liquid desiccant and dispensing dilute liquiddesiccant; a boiler for boiling partially preheated dilute liquiddesiccant to evaporate moisture to reconstitute the liquid desiccantinto concentrated liquid desiccant; and a condenser fluidlycommunicating with said boiler to receive steam generated by boilingliquid desiccant in said boiler without direct exposure to air saidcondenser further fluidly communicating with said absorber to receivedilute liquid desiccant from said absorber, said condenser beingoperable to sensibly heat the dilute liquid desiccant therein byrecovering the latent heat of condensation as steam delivered from saidboiler is condensed to preheat said dilute liquid desiccant prior todelivery to said boiler, said condenser including an air vent.
 7. Theliquid desiccant dehumidifier recited in claim 6 wherein said air ventcomprises a hydrophobic membrane enabling the free passage of air butpreventing liquid desiccant leakage.
 8. The liquid desiccantdehumidifier recited in claim 7, wherein said hydrophobic membrane tapeis laminated between a polypropylene mesh.
 9. The liquid desiccantdehumidifier recited in claim 6, wherein said air vent comprises afloat-type air vent.
 10. A liquid desiccant dehumidifier, comprising:aliquid desiccant absorber for absorbing moisture contained in ambientair entering the dehumidifier and passing through said desiccantabsorber, sand desiccant absorber constructed and arranged for receivingconcentrated liquid desiccant and dispensing dilute liquid desiccant; aboiler for boiling dilute liquid desiccant to evaporate moisture toreconstitute the liquid desiccant into concentrated liquid desiccant;and a condenser fluidly communicating with said boiler to receive steamgenerated by boiling liquid desiccant in said boiler, said condenserfurther fluidly communicating with said absorber to receive diluteliquid desiccant from said absorber, said condenser being operable tosensibly heat the dilute liquid desiccant therein by recovering thelatent heat of condensation as steam delivered from said boiler iscondensed and without directly exposing said dilute liquid desiccant toair so as to preheat said dilute liquid desiccant prior to delivery tosaid boiler, said condenser communicating with said desiccant absorberto recirculate a fraction of the liquid desiccant leaving said condenserto said desiccant absorber.
 11. A liquid desiccant dehumidifier,comprising:a liquid desiccant absorber for absorbing moisture containedin ambient air entering the dehumidifier and passing through saiddesiccant absorber, said desiccant absorber constructed and arranged forreceiving concentrated liquid desiccant and dispensing dilute liquiddesiccant, said desiccant absorber including a plurality of absorberpads bonded together and disposed side-by-side, said desiccant absorberfurther comprising a top distributor pan for distributing liquiddesiccant to a top side of said pads, and a drain pan for collectingdilute liquid desiccant from a bottom side of said pan; a boiler forboiling partially preheated dilute liquid desiccant to evaporatemoisture to reconstitute the liquid desiccant into concentrated liquiddesiccant, said boiler including an inner vessel and an outer vessel, aheating element disposed in said inner vessel, and a pipe communicatingheated liquid desiccant from said inner vessel and disposed within saidouter vessel, whereby liquid desiccant is returned to said outer vesselfrom said condenser and is heated in said outer vessel by hot liquiddesiccant passing through said pipe prior to entering said inner vessel;and a condenser fluidly communicating with said boiler to receive steamgenerated by boiling liquid desiccant in said boiler, said condenserfurther fluidly communicating with said absorber to receive diluteliquid desiccant from said absorber, said condenser being operable tosensibly heat the dilute liquid desiccant therein by recovering thelatent heat of condensation as steam delivered from said boiler iscondensed, to preheat said dilute liquid desiccant prior to delivery tosaid boiler, said condenser communicating with said desiccant absorberto recirculate a fraction of the liquid desiccant leaving said condenserto said desiccant absorber, said condenser further including an airvent.
 12. A liquid desiccant dehumidifier, comprising:a liquid desiccantabsorber for absorbing moisture contained in ambient air entering thedehumidifier and passing through said desiccant absorber, said desiccantabsorber constructed and arranged for receiving concentrated liquiddesiccant and dispensing dilute liquid desiccant, said desiccantabsorber including a plurality of absorber pads bonded together anddisposed side-by-side, said desiccant absorber further comprising a topdistributor pan for distributing liquid desiccant to a top side of saidpads, and a drain pan for collecting dilute liquid desiccant from abottom side of said pan; a boiler for boiling partially preheated diluteliquid desiccant to evaporate moisture to reconstitute the liquiddesiccant into concentrated liquid desiccant; and a condenser fluidlycommunicating with said boiler to receive steam generated by boilingliquid desiccant in said boiler, said condenser further fluidlycommunicating with said absorber to receive dilute liquid desiccant fromsaid absorber, said condenser being operable to sensibly heat the diluteliquid desiccant therein by recovering the latent heat of condensationas steam delivered from said boiler is condensed, to preheat said diluteliquid desiccant prior to delivery to said boiler, wherein saidcondenser comprises at least one tube assembly including an inner tubedefining a first flow passageway and an outer tube, said inner tubebeing disposed within said outer tube to define an annular second flowpassageway therebetween, wherein liquid desiccant is communicatedthrough a first of said flow passageways and steam is communicatedthrough a second of said flow passageways.
 13. The liquid desiccantdehumidifier defined in claim 12 wherein said inner tube comprises aconvoluted or corrugated tube.
 14. The liquid desiccant dehumidifierrecited in claim 13, wherein said tube assembly is coiled.